Use of multiple reticles in lithographic printing tools

ABSTRACT

A reticle stage having a range of motion sufficient to scan at least two distinct reticles. In a photolithographic process, a reticle stage having an extended range of motion and containing at least two reticles, preferably a phase shift reticle and a trim reticle, is used. The reticle stage scans the two reticles across an illumination field. The image of each reticle is projected by projection optics onto a photosensitive substrate on a wafer stage. The field on the photosensitive substrate is exposed with the image of the first reticle and subsequently exposed with the image of the second reticle. The projection of an image of a first and second reticle onto the same field in a scanning operation greatly facilitates throughput of the photolithographic tool or device. Reticle changes are eliminated when at least two reticles are needed to expose a single field. The use of multiple reticles to expose a single field is necessary when a phase shift mask and related trim mask are used. In another embodiment, the reticle stage has a range of motion permitting scanning of an additional calibration reticle. This permits rapid real time system calibration.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 09/785,777 (now U.S.Pat. No. 6,628,372 that issued Sep. 30, 2003), filed Feb. 16, 2001,which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates in general to photolithography used in themanufacture of semiconductor devices, and particularly to a reticlestage and method of increasing throughput.

BACKGROUND OF THE INVENTION

In the manufacture of semiconductor or electronic devices,photolithographic techniques or processes are often used. In thephotolithographic or lithographic process, a circuit pattern containedon a mask or a reticle is projected or imaged onto a photosensitivesubstrate.

The now patterned after processing photosensitive substrate is furtherprocessed to form a semiconductor or other electronic device by wellknown techniques. The substrate is typically a wafer. As the featuresizes required to be printed become smaller, different techniques forimaging the features become necessary. One technique for providing animproved quality of printing of the pattern is the use of a phase shiftmask or reticle. The use of a phase shift mask or reticle generallyrequires the exposure of the same field or area on a photosensitivesubstrate or wafer first with a phase shift mask and second with a trimmask. The trim mask is physically distinct from the phase shift mask andmay be printed with separate exposure conditions.

Accordingly, where the photolithographic process requires exposure ofthe same field on a photosensitive substrate with different masks, themasks must be changed between each exposure. This change greatly reducesthroughput and often creates potential alignment problems. A timeconsuming and potentially error prone alignment process must be done foreach mask used to expose the field on the photosensitive substrate orwafer. Accordingly, there is a need for a reticle stage and method forexposing the same field with at least two different masks or reticles ina manner to increase throughput and prevent alignment or calibrationproblems. There will always be a decrease in throughput as the wafer isessentially exposed twice. There is a need to eliminate this loss inthroughput to close to the unavoidable two exposure loss.

SUMMARY OF THE INVENTION

The present invention is directed to a reticle stage and method forincreasing throughput, and improving alignment when multiple masks orreticles are used during a double exposure of a field on aphotosensitive substrate. A reticle stage is used in a scanningphotolithographic tool or device comprising at least two masks orreticles. This invention can also be applied to a step and repeatsystem. The reticle stage has a range of motion permitting at least twomasks or reticles to be scanned sequentially exposing the same field totwo different patterns on a photosensitive substrate. In anotherembodiment, the reticle stage may have a third calibration reticleplaced adjacent to one of at least two masks or reticles. At least onephotosensitive substrate or wafer plane detector is used in combinationwith the calibration reticle or mask providing real time systemcalibration. The present invention is particularly suited for use withphase shift masks or reticles and associated trim masks or reticles.

Accordingly, it is an object of the present invention to provideincreased throughput when the system is used in a double exposure mode.

It is another object of the present invention to improve alignmentbetween exposures of the same field with at least two masks or reticles.

It is an advantage of the present invention that manufacturing costs arereduced.

It is a further advantage of the present invention that the same fieldcan be exposed with at least two masks or reticles without requiring amask or reticle change and realignment.

It is a feature of the present invention that a mask or reticle stage isused with at least two reticles or masks that has a range of motionpermitting scanning of the at least two masks or reticles.

It is another feature of the present invention that a calibrationreticle or mask is used in combination with at least one substrate orwafer plane detector.

These and other objects, advantages, and features will become readilyapparent in view of the following more detailed description.

IN THE DRAWINGS

FIG. 1A illustrates schematically a lithographic tool using multiplereticles or masks in a first position.

FIG. 1B illustrates schematically a lithographic tool using multiplereticles or masks in a second position.

FIG. 2 illustrates schematically a reticle stage having multiple masksor reticles thereon.

FIG. 3 illustrates schematically another embodiment of the presentinvention containing two masks or reticles.

FIG. 4 is a block diagram illustrating the method steps of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B schematically illustrates the present invention. FIG. 1Aillustrates the present invention in a first position, and FIG. 1Billustrates the present invention in a second position.

FIG. 1A illustrates a photolithographic system 10 used to project theimage of a mask or reticle 22 onto a photosensitive substrate 28. Theterms mask and reticle are intended to be equivalent, and meant to meana substrate, preferably glass or quartz, bearing a pattern, preferablyan integrated circuit, to be reproduced. An illumination system 12illuminates a mask or reticle 22 held within a mask or reticle stage 14.Associated with the illumination system 12 is an exposure parametermodifier 13 and an exposure control 15. The exposure parameter modifier13 is used to modify the exposure if needed. For example, the exposuredose or partial coherence may be modified between exposures as needed ordesired depending upon the required exposure needed to reproduce thepattern on the mask or reticle 22. This may be accomplished by anadjustable aperture or slit to adjust exposure dose or an array opticalelement to adjust partial coherence. Projection optics 18 project theimage of the reticle 22 onto a photosensitive substrate 28.Photosensitive substrate 28 is held on a wafer or substrate stage 16.The photosensitive substrate 28 may be a resist coated wafer. The maskor reticle stage 14 and the wafer or substrate stage 16 are controlledby stage control 20. The mask or reticle stage 14 scans in the directionof arrow 32 and the substrate or wafer stage 16 scans in the directionof arrow 34. The mask or reticle stage 14 contains at least two masks orreticles 22 and 24. In this embodiment, the reticle stage 14 alsocontains a calibration mask or reticle 26. The calibration mask orreticle 26 may be smaller than the mask or reticles 22 and 24, forexample, typically one-half the width in the scan direction, or in thedirection of arrows 32 and 34. For example, the masks or reticles 22 and24 may each have a width in the scan direction of approximately fifteencentimeters or six inches, while the calibration mask or reticle 26 hasa width in the scan direction of approximately eight centimeters orthree inches. The reticle stage 14 may be moved and has a range ofmotion that is at least equal to the width in the scanned direction ofthe masks or reticles 22 and 24. Additionally, the stage may have arange of motion to accommodate the calibration reticle 26, as well asany other additional range of scanning motion to accommodate anyengineering overscan allowances and the separation between masks orreticles 22, 24, and 26. One or more wafer or substrate plane detectoror detectors 30 may be placed on the wafer or substrate stage 16. Thewafer or substrate plane detector 30 detects specific patterns on thecalibration mask or reticle 26. This permits rapid real time systemcalibration. The wafer or substrate plane detector or detectors 30should be positioned such that it will receive the image of the patternson the calibration mask or reticle 26 during scanning of both the firstmask or reticle 22 and the second mask or reticle 24. Additionally, aseparate calibration alignment system may be used in conjunction withthe calibration mask or reticle 26 and the matched wafer or substrateplane detector or detectors 30.

FIG. 1B is similar to FIG. 1A, but illustrates the reticle stage 14 in asecond position for projecting the image of the mask or reticle 24 ontoa previously exposed field on the photosensitive substrate 28. Theexposed field on the photosensitive substrate 28 being previouslyexposed by an image of the mask or reticle 22, as illustrated in FIG.1A.

The invention is particularly adapted to, and intended to be used with,phase shift masks or reticles. For example, the first mask or reticle 22may be a phase shift mask or reticle, and the second mask or reticle 24may be a trim mask or reticle adapted to be used in combination with thephase shift mask or reticle. A phase shift mask or reticle and a trimmask or reticle are well known types of masks or reticles and commonlyused in photolithography. The phase shift mask or reticle and the trimmask or reticle are used to improve imaging, and in particular toenhance resolution.

Referring to FIGS. 1A and 1E, in operation the reticle stage 14 has thecapability and range to scan all three masks or reticles 22, 24, and 26across the illumination field 36 created by illumination system 12.Accordingly, the reticle stage 14 is scanned in the direction of arrow32 across the illumination field 36 created by the illumination system12. Synchronously, the wafer stage 16 is scanned in the direction ofarrow 34 to expose the photosensitive substrate or wafer 28 with theimage or pattern on the mask or reticle 22. The stage control 20controls this synchronization. Preferably, the projection optics 18provide a reduced image on the photosensitive substrate or wafer 28 ofthe pattern on the mask or reticle 22. Typically, a reduction ratio offour to one is used. This results in the reticle stage 14 scanning at arate four times that of the wafer stage 16. After this first or initialexposure of the photosensitive substrate or wafer 28 with the image orpattern contained on the mask or reticle 22, the wafer or substratestage 16 is repositioned for exposing the same field to the image orpattern on mask or reticle 24. Reticle stage 14 then continues scanningthe image of the mask or reticle 24 across the illumination field 26,exposing for a second time the same exposure field on the photosensitivesubstrate or wafer 28. Accordingly, the large overscan capability of thereticle stage 14, in combination with the at least two reticles 22 and24 contained thereon, enable both reticles to be maintained in positionwith no reticle change or realignment needed after initial alignment.This greatly increases throughput and eliminates any wasted time inhaving to change reticles and any required realignment after reticlechange or substitution. Additionally, by providing a scanning range ofmotion to include a calibrated mask or reticle 26, specific patterns maybe imaged onto one or more matched wafer or substrate plane detector ordetectors 30 to provide rapid real time system calibration.Additionally, any changes in the exposure conditions between the twotypes of masks, such as exposure, partial coherence, or other can bedone during a non exposure portion of the wafer print cycle and thus donot effect the throughput.

FIG. 2 is a plan view schematically illustrating the reticle stage 14.Reticle stage 14 is capable of scanning in the direction of arrow 32 andhas a range of motion at least equal to the cumulative width in the scandirection of masks or reticles 22, 24, and 26, plus any engineeringoverscan allowances that may be required. The range of motion of thereticle stage 14 must also be sufficient to accommodate the space or gapbetween each of the reticles or masks in the scan direction illustratedby arrow 32. The masks or reticles 22, 24, and 26 may be held within thereticle stage 14 by any conventionally known, or equivalent, reticleholding technique. Accordingly, illumination field 36 generally remainsstationary while the reticle stage 14 is scanned in the direction of thearrow 32 so as to sequentially expose the entire surface of all threemasks or reticles 22, 24, and 26.

FIG. 3 illustrates another embodiment of the present invention. In theembodiment illustrated in FIG. 3, a calibration reticle is not used.FIG. 3 is a plan view schematically illustrating a reticle stage 114.The reticle stage 114 is adapted to hold two related masks or reticles22 and 24. As previously indicated, reticle 22 may be a phase shift maskor reticle and mask or reticle 24 may be a trim mask or reticle to beused in combination with the phase shift mask or reticle 22. The reticlestage 114 has a range of motion such that the illumination field 36 isscanned in the direction of arrow 32 to illuminate both the masks orreticles 22 and 24.

FIG. 4 is a block diagram illustrating the method or process steps inthe present invention. Block 200 represents the step or act of holding afirst and second mask in a mask or reticle stage. The mask or reticlestage has a range of motion so that an illumination field can scan boththe first and second reticle. Block 202 represents the step or act ofpositioning a field on a photosensitive substrate to a first or initialposition. Block 204 represents the step or act of scanning an image ofthe first reticle onto the field. The first reticle is preferably aphase shift mask or reticle. Block 206 represents the step or act ofrepositioning the field that has been exposed by the first reticle tothe first position. Block 207 represents the step or act of adjusting anexposure parameter as needed between the exposure of the first reticleand the second reticle. The exposure parameter may be the exposure doseor partial coherence. The partial coherence may be changed by changingthe numerical aperture of the illumination system or the angularproperties of the illumination. Block 208 represents the step or act ofscanning an image of the second reticle onto the field. The secondreticle is preferably a trim mask or reticle that is matched orcomplements the phase shift mask or reticle. The field previouslyexposed with an image of the first reticle is re-exposed with an imageof the second reticle. The use of a phase shift mask and a trim maskadapted to be used with the phase shift mask improves imaging, andparticularly resolution.

The present invention greatly facilitates the exposure of at least tworeticles in a scanning photolithographic system or tool. The presentinvention is also particularly adapted for use with a phase shift maskand corresponding trim mask for sequentially exposing the same field ona photosensitive substrate. The time consuming step of changing masks orreticles on a reticle stage is therefore eliminated. Additionally, inone embodiment the use of a calibration reticle or mask and a reticlestage having a range of motion encompassing the calibration reticle ormask makes possible rapid real time system calibration. Therefore, thepresent invention greatly facilitates and advances the art of electronicdevice manufacturing. While the present invention has been illustratedand described with respect to several embodiments, in particular anembodiment having a range of motion to accommodate three differentreticles, it should be appreciated that other numbers of reticles may beutilized, provided at least two of the reticles are used to expose thesame field with a reticle stage having a range of motion sufficient toscan the at least two reticles or masks. Additionally, it will beobvious to those skilled in the art that various modifications may bemade without departing from the spirit and scope of this invention.

What is claimed is:
 1. A method of sequentially exposing a field with animage of first and second reticles comprising: simultaneously holdingthe first and second reticles and a calibration reticle on a reticlestage; positioning the field in an exposure position; scanning an imagefrom the first reticle to expose the field; repositioning the field tothe exposure position; and scanning an image from the second reticle toexpose the field.
 2. The method of claim 1, further comprising:detecting an image of the calibration reticle; and calibrating thesystem based on the detecting.
 3. The method of claim 2, furthercomprising performing the calibrating in real time.
 4. The method ofclaim 1, further comprising: adjusting an exposure parameter betweenexposing the first and second reticles.
 5. The method of claim 4,wherein: the exposure parameter comprises exposure dose.
 6. The methodof claim 4, wherein: the exposure parameter comprises partial coherence.7. The method of claim 1, further comprising: using a phase shiftreticle as the first reticle; and using a trim reticle as the secondreticle.